The risk of extensive alcohol use is increased during adolescence, and attractiveness of ethanol at this age is based in part on its properties to produce social facilitation, since adolescence as a developmental period is characterized by a high significance of interactions with peers and high social motivation. An attenuated sensitivity to adverse effects of ethanol that normally serve to diminish drinking (including ethanol-induced social inhibition) could serve as a permissive factor for heavy drinking during adolescence. Animal studies have shown that adolescent rats, like their human counterparts, are extremely sensitive to activating effects of ethanol on social behavior and relatively insensitive to ethanol-induced behavioral suppression and social inhibition. Considerable ontogenetic differences in the social consequences of ethanol are evident even within the adolescent period, with early adolescence being a time of particularly pronounced adolescent-typical sensitivities to ethanol. In adult animals, endogenous opioid mechanisms have been shown to be involved in mediation of ethanol effects, with positive (stimulatory and reinforcing) properties of ethanol being related to mu receptors and adverse (aversive and inhibitory) effects of the drug being associated with kappa receptors. The present proposal uses an animal model of peer-directed social activity to investigate whether these opposing opioid mechanisms are likewise involved in mediation of the social consequences of ethanol and whether adolescent animals are more sensitive than adults to ethanol- induced activation of the mu opioid system and less sensitive than their adult counterparts to activation of the kappa opioid system. Using a psychopharmacological approach with receptor-selective opioid antagonists and agonists, experiments will be conducted to determine the effectiveness of opioid antagonists in reversing ethanol-induced social facilitation and social inhibition, and to compare the social consequences of opioid agonists in early, mid, and late adolescent as well as adult rats with previously characterized ontogenetic patterns of responsiveness to the stimulatory and inhibitory effects of ethanol on social behavior. The proposed work will provide information about substrates underlying the age-specific sensitivities of young adolescents to the social consequences of ethanol and their potential implications regarding the frequent initiation of ethanol use and high consumption levels at this age.